I read something recently that made this claim. The author characterized the hoplites as simple farmers who earned enough to buy a helmet and shield and sword to be able to fight wars for Greece. These hoplites were not the wealthiest Greeks, but they were a major part of the fighting ranks.
Because these hoplites were risking their lives for wars that gave greater wealth to others, this author argued, these hoplites eventually insisted on a more democratic control over Greece and its distribution of wealth. So, the author concludes, democracy in ancient Greece arose in response to increasing concentrations of wealth at the expense of those who demanded greater democracy.
Is this a fair reading of the historical record for ancient Greece?
Although he might have more to say, /u/iphikrates has written extensively on Victor Davis Hanson and his theory about the middle class hoplite:
Victor Davis Hanson and the question of the middle-class infantrymen
How is Victor Davis Hanson's work on Greek warfare viewed within ancient warfare studies